12/5/2012 11:31 PM, Jonathan M Davis пишет:
On Wednesday, December 05, 2012 22:07:48 Dmitry Olshansky wrote:
12/5/2012 5:40 AM, Jonathan M Davis пишет:
There's nothing natural about Variant. It's attempting to add dynamic
typing to a statically typed language.
Bleh that smells religious. There are cases where one may just go for it
to simplify matters. Spreadsheets, Db rows and whatnot often operate in
Variants. Simply because one can't know ahead of time what the content
is in a arbitrary DB.
Yes, but that inevitably forces you to check the type in order to handle it
correctly, which means that implicit conversion just doesn't work. In order
for implicit conversion to work, you have to be able to assume that you're
dealing with a particular type, and if you can do that, why are you using a
Variant in the first place? Just use a common type.
Simply put it's the API that is more flexible the your concrete code.
But there is a point in forcing the expected types as soon as possible.
In other words it's a sugar for calling Varaint.get for the type on the
right. That's where the point that you don't like it while I think it
could be handy.
And as you can't know what it's type really is
at compile time, all conversions require type checking at runtime. And
implicit conversions must be determined at compile time. So really, the
implicit conversions make no sense at all.
And I would generally expect that
code would have to check the type of a Variant before doing a conversion -
to do what? throw an Exception?? :)
To know what on earth you're suposed to do with the variable. If it's a type
that you can't handle, then yes, you'd probably have to throw an exception,
but you generally use a Variant because you need to be able to return multiple
types from the same function, and each is going to be treated differently,
otherwise you could have just used a common type to begin with.
This is a sort of case against Varaint at large.
I just don't see how it makes any sense to implicitly convert a Variant when
the only reason to use a Variant is if the types involved have no common type.
Since if they no common type, you're going to have to check what it is to know
what you can validly do with it.
It's not. If the only reason was that I'd use an opaque "box" type.
--
Dmitry Olshansky
